The present invention generally relates to an image forming apparatus such as a copying apparatus and the like, and more particularly, to a multi-color image forming apparatus having a function for reproducing an image of an original document in a plurality of colors.
Conventionally, as one type of a multi-color image forming apparatus, there has been proposed a copying apparatus in, for example, U.S. Pat. No. 3,914,043. In this known copying apparatus, there is provided at a side of an original platform of glass disposed at an upper portion of an apparatus housing, a region designating means not only for designating a plurality of regions by dividing a face of the original platform in a scanning direction of an exposure lamp but for designating reproduction colors of portions of an image of an original document located at the regions, respectively.
In the case where the image of the original document is reproduced in two colors by using this known copying apparatus, the image of the original document is initially scanned by the exposure lamp such that an electrostatic latent image is formed on a surface of a photoreceptor or photosensitive drum. Then, by leaving only an electrostatic latent image portion corresponding to a first designated region as it is, another electrostatic latent image portion corresponding to the remaining region is erased. Thereafter, the first designated region is reproduced by developer of a first designated color. Subsequently, this image of the first color is transferred onto a copy paper sheet and then, is subjected to fusion fixing in a fixing process.
Then, the image of the original document is scanned by the exposure lamp again such that the electrostatic latent image is re-formed. By leaving only an electrostatic latent image portion corresponding to a second designated region as it is, another electrostatic latent image portion corresponding to the remaining region is erased. Thereafter, the second designated region is reproduced by developer of a second designated color. This image of the second color is transferred onto the copy paper sheet bearing the image of the first color and then, is again subjected to a fixing operation so as to be discharged from the apparatus housing.
As described above, in the known copying apparatus, copying operations should be repeated times of the number identical with the number of the reproduction colors.
Thus, the known copying apparatus has such a drawback that a long time period is required for copying. Furthermore, when the image of the first color is fixed in the fixing process, the copy paper sheet is subjected to thermal shrinkage by high temperature and timing of the first feed of the leading edge of the copy paper sheet to the transfer zone deviates from that of the second feed, such a problem arises that an improper image is formed through overlap between the image of the first color and the image of the second color or formation of blank portions therebetween.